In one class of fuel injectors, a reciprocating plunger is utilized to pressurize fuel to initiate and sustain injection. With each reciprocation, pressure gradients along the plunger can oscillate between zero and about twenty thousand psi or more at a frequency of many times per second. Because of this high cyclic pressure gradient, fuel naturally has the tendency to leak past the plunger along the plunger bore wall. For a number of reasons, including decreased complexity, increased reliability, allowable fuel leakage, concerns about where and how to route the leaked fuel and for other reasons known to those skilled in the art, it is often desirable to eliminate leakage past the plunger by using an O-ring seal. However, because of the high frequencies involved in injection cycles and the extreme magnitude of cyclic pressure changes acting on an O-ring seal, most presently available O-rings tend to fail long before the other components of the fuel injector. In other words, O-ring technology has not sufficiently advanced to provide reliable and long term sealing at the high frequencies and relatively extreme pressures experienced within a fuel injector environment.
One response to this problem has been to include a pressure receiver volume at a position between the O-ring and the pressure face end of the plunger. This pressure receiver volume typically takes the form of an annulus machined in the side wall of the plunger below the O-ring but above the pressure face end of the plunger. Cyclic pressures on the O-ring are substantially attenuated by the inclusion of a pressure receiver volume since a substantial amount of the high pressure in each injection cycle is absorbed in the receiver volume before the same ever reaches the O-ring seal. Pressure in the receiver volume drops or resets itself when the plunger is undergoing its return stroke between injection events. One problem associated with the simple use of a receiver volume to attenuate pressures on the O-ring is the need to make the volume relatively large in order to provide a satisfactory attenuation on the pressures experienced by the O-ring seal. In other words, more pressure attenuation can be provided by making the receiver of volume ever larger; however, realistic space constraints and plunger guiding considerations, among other things, limit the realistic amount of volume that can be devoted to the pressure receiver volume space.
The present invention is directed to overcoming this and other problems associated with sealing against fluid leakage past a reciprocating plunger within a fuel injector.